The present invention relates to cutting, milling, and turning tools and more particularly to improving the performance of cubic boron nitride (cBN) superabrasive tools for material removal operations.
The manufacture of cBN by the high pressure/high temperature (HP/HT) process is known in the art as described in U.S. Pat. Nos. 2,947,617. 4,188,194 describes a process for making sintered polycrystalline cBN compacts, which utilizes pyrolytic hexagonal boron nitride (PBN) in the absence of any catalyst. An improvement on such direct conversion process is disclosed in U.S. Pat. No. 4,289,503, wherein boric oxide is removed from the surface of the HBN powder before the conversion process.
A compact is a mass of abrasive particles bonded together in a self-bonded relationship, by means of a bonding medium, or by means of combinations thereof. A composite compact is a compact bonded to a substrate material, such as cemented metal carbide. U.S. Pat. No. 3,918,219 teaches the catalytic conversion of hexagonal boron nitride (HBN) to cBN in contact with a carbide mass to form a composite cBN compact. Compacts or composite compacts may be used in blanks for cutting tools, drill bits, dressing tools, and wear parts.
Polycrystalline cBN compacts often are used in machining hard ferrous alloy workpieces. Tool hardness and mechanical properties must be balanced against tool reactivity. High cBN content compacts provide the highest hardness, but, generally, are reactive towards alloy steels. To provide utility, non-reactive phases often are added to protect the cBN from reacting with ferrous alloys.
There are a number of references teaching various compositions for high pressure and temperature sintered bodies made from cubic boron nitride (cBN) and transition metal nitrides or carbides.
U.S. Pat. No. 4,334,928 describes sintered bodies containing 20-80 volume-% cBN and a binder phase consisting of carbides, nitrides, carbo-nitrides, suicides, or borides of the metals in groups IV and V of the periodic table. The addition of aluminum to the binder phase also is included. The Ti compounds added to the mixture preferably have a stoichiometry such that the value of xe2x80x9czxe2x80x9d is less than 0.97 for the general formula: Ti(X)z where xe2x80x9cXxe2x80x9d is carbon or nitrogen or combinations of the two.
U.S. Pat. No. 4,343,651 describes sintered bodies wherein the material contains 80-95% by volume cubic boron nitride.
U.S. Pat. No. 4,911,756 describes sintered bodies made from a sinter mix that contains 50-75 volume-% cBN and 25-50 volume-% of a binder phase. The binder phase consists of 20-50 weight-% Al or Al compounds, carbides, nitrides, carbo-nitrides, silicides, or borides of the metals in groups IV, V and VI of the periodic table (including Ti and W), wherein the Ti compounds added are stipulated to have a stoichiometry such that the value of xe2x80x9czxe2x80x9d is within the range of 0.5 to 0.85 for the general formula: Ti(X)z where xe2x80x9cXxe2x80x9d is carbon or nitrogen or combinations of the two.
U.S. Pat. No. 5,092,920 describes sintered bodies with 45-0 volume-% cBN with average particle size of 2 microns or less with a binder phase comprised of 5-15 weight-% of aluminum, 2-20 weight-% of tungsten, and the remainder being any of the prior mentioned Ti compounds, where the stoichiometry of the Ti compounds is such that the value of xe2x80x9czxe2x80x9d is within the range of 0.45-0.65 for the general formula: Ti(X)z where xe2x80x9cXxe2x80x9d is carbon or nitrogen or combinations of the two.
U.S. Pat. No. 6,316,094 describes sintered bodies comprised of45-70 volume-% cBN with a grain size of 2 to 6 microns with a 2-dimensionally continuous binding phase comprised of at least one of the following: a carbide, nitride, carbo-nitride, or boride of a group IVB, VB or VIB transition metal (including Ti and W), a nitride, boride, or oxide of aluminum, a carbide, nitride, carbo-nitride or boride of iron, cobalt, or nickel, and solid solutions thereof. It is also stipulated that the binder phase has an average thickness of 1.5 microns or less with a standard deviation of 0.9 microns or less.
Thus, while improvements have been realized by the foregoing approaches, an optimized product is required for each chemical class of alloy materials to be machined. Increased development costs and product line support costs add to the cost of such cBN machining products. Applicants have found an optimized sintered compact composition comprising tungsten compounds and cBN grains having a volumetric mean particle size of greater than 2 microns, for an improved machining performance.
The sintered compact of the present invention is obtained by sintering a mixture of about 60-80 percent by volume of cubic boron nitride (cBN) with the cBN grains have a volumetric mean particle size between 3 and 6 xcexcm, about 20-40 vol-% of a ceramic binder phase under high pressure and temperature conditions; wherein the binder phase is between about 20 and 60 vol-% of one or more of carbides, nitrides, or borides of the metals of groups IVB and VIB of the periodic table, and between about 40 and 80 vol-% of one or more of carbides, nitrides, borides, or oxides of aluminum; and about 3 to 15 wt % tungsten. Other Iron group metals, in the form of a carbide or boride also may be present as impurities introduced by processing.
The present invention further relates to forming tools comprising cBN compacts containing a mixture of about 60-80 percent by volume of cubic boron nitride (cBN) with the cBN grains have a volumetric mean particle size between 3 and 6 xcexcm, about 20-40 vol-% of a ceramic binder phase, and about 3 to 15 wt-% tungsten.